VO₂ powders and VO₂/graphene composite powders were prepared by using hydrothermal reaction and thermal treatment with vanadyl oxalate solution as the vanadium source, sodium tungstate as the dopant and graphene oxide as the additive. With the assistance of XRD, DSC and TEM analyses, the effects of hydrothermal reaction conditions, doping amount and graphene oxide addition on structure and morphology, phase transition temperature and thermochromic properties the powders were systematically studied. Within the experimental temperature range, property of the hydrothermal reaction product is independent on the hydrothermal temperature, but is directly related to the hydrothermal time. The phase transitions of VO₂(D) and VO₂(B) to VO₂(M) during the thermal treatment occurred at 300 ℃ and 550 ℃, respectively. Tungsten doping resulted in reduction in thermochromic temperature and thermal hysteresis temperature difference of the VO₂ powders. With increasing content of graphene oxide, the thermochromic temperature first decreased and then increased, while the variation trend of thermal hysteresis temperature difference is the opposite. With the doping concentration of 9 at.% and graphene oxide content of 1 wt.%, the doped VO₂/graphene composite powder exhibited a thermochromic temperature of 34.5 ℃ and a thermal hysteresis temperature difference of 7.7 ℃.

Porous glass-ceramics were prepared by using a two-step sintering process, i.e., low-temperature sintering and high-temperature foaming, with granite powder as the raw material and SiC as the foaming agent. The effects of sintering and foaming temperature on pore structure, crystal phase composition and compressive strength of the porous glass-ceramics were systematically studied by using XRD, SEM, TG-DSC and ceramic bending tester. Foaming mechanism of the glass-ceramics was analyzed. With increasing sintering temperature, flexural strength and bulk density of the glass-ceramics without foaming agent first increased and then decreased, while the optimum sintering temperature was 1120 ℃. With increasing foaming temperature, anorthite and quartz in the glass-ceramics gradually dissolved into the glass phase. Meanwhile, the crystallinity decreased, the pore size increased, and both the apparent density and compressive strength decreased. However, the specific strength reached a maximum value of 5.36 kN·m·kg^-1 at 1220 ℃, with a porosity of 59.7%. In contrast to the open pore structure of the one-step sintered sample, the two-step sintered sample shows a closed pore structure. Specific strength of the porous glass-ceramic prepared by using the two-step sintering is superior to that of sample prepared by using the one-step sintering method.

The oyster cultivation in coastal areas of China produces a large number of oyster shells every year, whose resource utilization is related to environmental protection and sustainable development of industry. Lightweight oyster shell-based geopolymers were prepared by using oyster shell and fly ash as main raw materials, water glass and NaOH solution as composite activators, and H₂O₂ as the foaming agent. The effects of foaming agent, aluminum silicate fiber and calcium stearate on pore structure, apparent density, compressive strength and weathering properties of the oyster shell geopolymers were systematically studied. The pore structure and microstructure were analyzed by using XRD, FTIR, SEM and contact angle tester. It is found that apparent density and compressive strength of the geopolymer continue to decrease with increasing content of H₂O₂, but the strength increases first and then decreases. Apparent density, compressive strength and specific strength of the geopolymers increase first and then decrease with increasing content of aluminum silicate fiber, reaching the maximum values at 1.00%, which are 0.63 g·cm⁻³, 4.45 MPa and 6.98 kN·m·kg⁻¹, respectively. The addition of a small content of calcium stearate did not affect structure and compressive strength of the geopolymers, the weathering performance was significantly improved. When the content was 0.50%, the optimal weight loss and specific strength loss were 10.1% and 14.1%, respectively. This lightweight geopolymer is expected to be useful in sidewalk bricks and curb stones to realize the value-added utilization of oyster shells as resources.

Porous glass-ceramics were derived from surface-modified pickling copper mine tailing powder with boehmite sol(1 wt.%) as the sintering additive and SiC (0-5.0 wt.%) as the foaming agent. The effect of SiC on pore structure, compressive strength and thermal conductivity of the glass-ceramics were systematically studied. With increasing content of SiC, the pores generated by the blowing agent in the porous glass-ceramics gradually connected and coalesced with the residual pores in the matrix to form larger pores. The porosity first increased and then decreased, the compressive strength and specific strength continued to decrease, and the thermal conductivity first decreased and then increased. With 2.0 wt.% SiC, the porosity of porous glass-ceramics is 45.6%, while the compressive strength and thermal conductivity are 60.4 MPa and 0.828 W·m^-1·K^-1, respectively. The theoretical value of thermal conductivity is higher than the measured value at low porosity, while the theoretical value is basically the same as the measured value at high porosity, indicating that the pores are of closed structure after coalescence. These red porous glass-ceramics are suitable for lightweight decorative building materials, thus realizing the value-added utilization of copper mine tailings.